131I-metaiodobenzylguanidine (131I-MIBG) is a norepinephrine analog that concentrates in adrenergic tissue and therefore holds promise for cell-specific treatment of neuroblastoma. This is a dual institution, Phase II study of 131I-MIBG administered at the previously defined maximum practical dose of 18 mCi/kg to children with relapsed or refractory neuroblastoma.